The 5.1-rc1 release is based on the Android 5.1.1_r24. We added many x86 specified code and fixed issues to let the system runs smoothly on x86 platforms, especially for netbooks or tablets. The key features contain
We create universal images for most x86 platforms. This release contains two files. One is the 32-bit x86 ISO and the other is the 64-bit x86_64 ISO. Both can be boot from legacy BIOS and newer UEFI firmware. You can choose one of them depends on your devices. In doubt, try the 32-bit ISO for legacy BIOS devices and 64-bit ISO for UEFI devices.
sha1sum: 33d1489195e8ca3e9b9c253848181e9cb5b311bf
sha1sum: 56d559d186033a840076d0517ecb89d3c8cc46b5
Both files can be dumped into a usb drive to create a bootable usb stick like :
dd if=android-x86-5.1-rc1.iso of=/dev/sdX
where /dev/sdX is the device name of your usb drive.
repo init -u git://git.osdn.net/gitroot/android-x86/manifest -b lollipop-x86
repo sync
Read this page for how to compile source code.